tsp问题——遗传算法解决

小鱼儿 2022-08-04 08:29 192阅读 0赞

TSP问题最简单的求解方法是枚举法。它的解是多维的、多局部极值的、趋于无穷大的复杂解的空间，搜索空间是n个点的所有排列的集合，大小为（n-1）！。可以形象地把解空间看成是一个无穷大的丘陵地带，各山峰或山谷的高度即是问题的极值。求解TSP，则是在此不能穷尽的丘陵地带中攀登以达到山顶或谷底的过程。

这一篇将用遗传算法解决TSP问题。

1）评价。这个评价算法应该比较简单了，就是找计算总距离，小的为优。目标函数转化为适应度函数可以取倒数。

2）突变。为了防止重复访问，不能随机的进行突变。因为每个城市只能访问一次，我们只需要任意的交换两个城市即可。

![swap_mutation.jpg][]

上一行是突变之前，下面一行是突变之后的。

3）交叉。这个操作是个比较关键的步骤，怎样交叉才能才能父母的优秀基因呢？对于TSP问题，我们要找的是一个最优的排列，其中排列的顺序应该是最重要的。

因此在交叉的时候，分别随机的取 父母的部分序列，要保持原有的顺序。

Parents

![crossover_parents.jpg][]

先随机的选取 Parent1 的 一部分，例如 678 部分，。然后把剩下的城市 安装 Parent2 中的顺序，遗传下去。

Chlid

![crossover_children.jpg][]

其它基本按照遗传算法的框架来就行了

// TSP.cpp : 定义控制台应用程序的入口点。
    //
    
    #include "stdafx.h"
    #include<iostream>
    //#include <stdio.h>
    #include <time.h>
    //#include <stdlib.h>
    
    using namespace std;
    #define   POPSIZE      200   //种群总数
    #define rdint(i)(rand()%(int)(i))
    #define rdft()((float)rdint(16384)/(16383.0))
    typedef unsigned char BYTE;
    
    //31个城市的坐标
    int city[31][2] = { { 1304, 2312 }, 3639, 1315, 4177, 2244, 3712, 1399, 3488, 1535, 3326, 1556, 3238, 1229,
    4196, 1004, 4312, 790, 4386, 570, 3007, 1970, 2562, 1756, 2788, 1491, 2381, 1676, 1332, 695, 3715, 1678,
    3918, 2179, 4061, 2370, 3780, 2212, 3676, 2578, 4029, 2838, 4263, 2931, 3429, 1908, 3507, 2367, 3394, 2643,
    3439, 3201, 2935, 3240, 3140, 3550, 2545, 2357, 2778, 2826, 2370, 2975 };
    
    int* my_unrepeat_rand(int L, int H)
    {
    	const int LEN = H - L + 1;
    	//int n[LEN];
    	int *n = new int[LEN];
    	for (int i = 0; i < LEN; ++i)
    	{
    		n[i] = L + i;
    	}
    	
    	for (int j = LEN; j > 0; --j)
    	{
    		int m = j*rand() /(RAND_MAX + 1.0);
    		int temp = n[m];
    		n[m] = n[j - 1];
    		n[j - 1] = temp;
    	}
    	return n;
    }
    
    
    
    class Chromosome
    {
    	friend class Population;
    public:
    	static const int length = 31;
    	
    private:
    	BYTE gene[length];
    	double fitness;
    	double distance;
    public:
    	void initial_chromosome()//初始化染色体
    	{
    		distance = 0;
    		fitness = 0;
    		int*b = my_unrepeat_rand(0, length - 1);
    		for (int i = 0; i < length; i++)
    			gene[i] = b[i];
    		delete[]b;
    	}
    	BYTE*get_gene()
    	{
    		return this->gene;
    	}
    	double get_distance()
    	{
    		return distance;
    	}
    	void calculate_distance()//计算适应度，这里直接取总距离，越小越好
    	{
    		distance = 0;
    		for (int i = 0; i < length - 1; i++)
    		{
    			distance += sqrt(pow(double(city[gene[i]][0] - city[gene[i + 1]][0]), double(2)) + 
    				pow(double(city[gene[i]][1] - city[gene[i + 1]][1]), double(2)));
    		}
    		distance += sqrt(pow(double(city[gene[0]][0] - city[gene[length - 1]][0]), double(2)) + pow(double(city[gene[0]][1] - city[gene[length - 1]][1]), double(2)));
    	}
    
    	pair<Chromosome, Chromosome> cross(Chromosome p1)//交叉操作，选中区间的基因不改变，孩子基因的其他位置的基因从配偶处获得，要保持顺序
    	{
    		pair<Chromosome, Chromosome>child;
    		//srand(time(0));
    		int m = rand() % length ;
    		int n = rand() % length;
    		if (m > n)
    		{
    			int temp = m;
    			m = n;
    			n = temp;
    		}
    		int j = 0,p=0;
    		for (int i = 0; i < length; i++)
    		{
    			if (i >= m&&n >= i)
    			{
    				child.first.gene[i] = gene[i];
    				child.second.gene[i] = p1.gene[i];
    				continue;
    			}
    			bool flag = true;
    			while (flag)
    			{
    				flag = false;
    				for (int k = m; k <= n; k++)
    					if (p1.gene[j] == gene[k])
    					{
    					flag = true;
    					break;
    					}
    				if (flag)
    					j++;
    			}
    			child.first.gene[i] = p1.gene[j];
    			j++;
    			flag = true;
    			while (flag)
    			{
    				flag = false;
    				for (int k = m; k <= n; k++)
    					if (gene[p] == p1.gene[k])
    					{
    					flag = true;
    					break;
    					}
    				if (flag)
    					p++;
    			}
    			child.second.gene[i] = gene[p];
    			p++;
    		}
    
    		return child;
    	}
    
    	Chromosome mutation()//变异，选择两个位置交换基因
    	{
    		int m = rand() % (length - 1);
    		int n = rand() % (length - 1);
    		while (n == m)
    		{
    			n = rand() % (length - 1);
    		}
    		int temp = gene[m];
    		gene[m] = gene[n];
    		gene[n] = temp;
    		return *this;
    	}
    
    };
    
    
    
    class Population
    {
    private:
    	Chromosome pop[POPSIZE];
    	Chromosome best;
    	Chromosome worst;
    	unsigned int Generation;
    	unsigned int maxgeneration;
    	double m_dCrossoverRate;//交叉率0.6
    	double m_dMutationRate;//变异率0.01
    	bool elitism;//是否在新一代中保存前一代的最优个体
    	double m_dTotalFitnessScore;
    	void initial_pop()
    	{
    		for (int i = 0; i < POPSIZE; i++)
    			pop[i].initial_chromosome();
    	};
    public:
    	Population(double pc, double pM, bool ISelitism, unsigned int maxgen) :m_dCrossoverRate(pc), m_dMutationRate(pM), elitism(ISelitism), maxgeneration(maxgen)//构造函数
    	{
    		Generation = 1;
    		initial_pop();
    	}
    	void Calcu_fit()//计算适应值
    	{
    		m_dTotalFitnessScore = 0;
    		for (int i = 0; i < POPSIZE; i++)
    		{
    			pop[i].calculate_distance();
    		}
    		find_best_worst();
    		//sort_by_distance(POPSIZE);
    		double mindis = best.distance;
    		double maxdis = worst.distance;
    		for (int i = 0; i < POPSIZE; i++)
    		{
    			pop[i].fitness = 1 - (pop[i].distance - mindis) / (maxdis - mindis + 0.0001);//double(1000) / pop[i].distance;//
    			m_dTotalFitnessScore += pop[i].fitness;
    		}
    
    	}
    	//fitness(i,1)=(1-((len(i,1)-minlen)/(maxlen-minlen+0.0001)))
    	void sort_by_distance(int k)
    	{
    		if (k == 1)
    			return;
    		for (int i = 0; i < k-1; i++)
    		{
    			if (pop[i].distance < pop[i + 1].distance)
    			{
    				double temp = pop[i].distance;
    				pop[i].distance = pop[i + 1].distance;
    				pop[i + 1].distance = temp;
    			}
    		}
    		sort_by_distance(k - 1);
    	}
    	void find_best_worst()
    	{
    		double mindis = 100000000;
    		double maxdis = 0;
    		for (int i = 0; i < POPSIZE; i++)
    		{
    			if (pop[i].distance > maxdis)
    			{
    				maxdis = pop[i].distance;
    				worst = pop[i];
    			}
    			if (pop[i].distance < mindis)
    			{
    				mindis = pop[i].distance;
    				best = pop[i];
    			}
    		}
    	}
    	
    
    	int RouletteWheelSelection()
    	{
    		double fSlice = rdft() * m_dTotalFitnessScore;
    		double cfTotal = 0.0;
    
    		for (int i = 0; i<POPSIZE; ++i)
    		{
    			cfTotal += pop[i].fitness;
    			if (cfTotal > fSlice)
    			{
    				return i;
    			}
    		}
    	}
    	void Epoch()
    	{
    		Calcu_fit();
    		Chromosome new_pop[POPSIZE+1];
    		int NewBabies = 0;
    		if (elitism)
    		{
    			NewBabies = 1;
    			new_pop[0] = best;
    		}
    		
    		while (NewBabies < POPSIZE)
    		{
    			//select 2 parents
    			int mum = RouletteWheelSelection();
    			int dad = RouletteWheelSelection();
    			while (dad == mum)
    			{
    				dad = RouletteWheelSelection();
    			}pair<Chromosome, Chromosome>child;
    			if (rdft() < m_dCrossoverRate)
    			{
    				child = pop[mum].cross(pop[dad]);
    			}
    			else
    			{
    				child.first = pop[mum];
    				child.second = pop[dad];
    			}
    			if (rdft() < m_dMutationRate)
    			{
    				child.first.mutation();
    			}
    			if (rdft() < m_dMutationRate)
    			{
    				child.second.mutation();
    			}
    			new_pop[NewBabies]=child.first;
    			new_pop[NewBabies+1] = child.second;
    			NewBabies += 2;
    		}
    
    		for (int i = 0; i < POPSIZE; i++)
    			pop[i] = new_pop[i];
    		++Generation;
    	}
    	
    	Chromosome get_best()
    	{
    		return best;
    	}
    	void run()
    	{
    		while (Generation < maxgeneration)
    		{
    			Epoch();
    		}
    	}
    
    };
    
    int _tmain(int argc, _TCHAR* argv[])
    {
    	time_t t;
    	srand((unsigned)time(&t));
    	
    
    	Population tsp(0.6,0.1,true,1000);
    	tsp.run();
    
    	cout << tsp.get_best().get_distance()<<endl;
    	system("pause");
    	return 0;
    }

[swap_mutation.jpg]: /images/20220731/9c8a4055070144578440acbb498a7fec.png
[crossover_parents.jpg]: /images/20220731/15953f316102404f945022bcb06ae367.png
[crossover_children.jpg]: /images/20220731/4229dc13cd8640808c5462da034a6653.png